The present invention relates to an image recording apparatus using a pressure sensitive sheet. More particularly, the invention relates to a pressure developing device in the image recording apparatus for developing a latent image on a pressure-sensitive recording sheet and transferring the image as a visible image onto a developer sheet, under pressure. The invention also relates to a sheet feeding mechanism for feeding a web like pressure sensitive recording sheet for use in the image recording apparatus.
U.S. Pat. No. 4,440,846 discloses an image recording system in which a developer sheet and a photosensitive pressure-sensitive recording sheet exposed to light bearing a latent image are superposed on each other and pressed together to develop the image on the developer sheet. The photosensitive pressure-sensitive recording sheet has a coated layer of pressure-rupturable microcapsules encapsulating a photosensitive composition. Such image forming technique is generally referred to as transfer type image recording method in which the developer material is coated on a substrate such as a developer sheet, which developer material is reacted with encapsulated chromogenic material provided on a separate sheet as described in U.S. Pat. No. 4,399,209.
Generally, the photosensitive pressure-sensitive recording sheet is in the form of a roll, and the developer sheet is in the form of a cut sheet. The photosensitive pressure-sensitive recording sheet is normally gripped or nipped between a pair of pressure developing means or rollers. When microcapsules on the photosensitive pressure-sensitive recording sheet are ruptured by being pressed between the pressure developing rollers, the photosensitive composition is released from the ruptured microcapsules. One problem with the conventional arrangement is that the released photosensitive composition tends to be attached to the surfaces of the pressure developing rollers.
In another aspect, the photosensitive pressure-sensitive recording sheet is fed by either a takeup roll which pulls the recording sheet or a pair of feed rollers which grip and feed the opposite side edges of the web like recording sheet. Feeding the photosensitive pressure-sensitive recording sheet with the takeup roll is disadvantageous in that as the photosensitive pressure-sensitive recording sheet is wound on the takeup roll, the diameter of the takeup roll is progressively increased and the speed at which the recording sheet is fed is progressively increased so far as the takeup roll is rotated at constant angular velocity. As a result, the latent image on the photosensitive pressure-sensitive recording sheet, which latent image is formed by the light-exposure to an original, may be distorted or the exposed area on the photosensitive pressure-sensitive recording sheet may be brought out of exact registry with the developer sheet, to thereby degrade the resultant final visible image on the developer sheet.
It would be possible to control the speed at which the recording sheet is wound on the takeup roll in accordance with the diameter of the takeup roll. However, this would require a sensor for detecting the speed of travel of the photosensitive pressure-sensitive recording sheet as well as a highly accurate speed-controllable motor for driving the takeup roll, resulting in an increased cost of manufacture.
On the other hand, where the feed rollers are used to grip the side edges of the photosensitive pressure-sensitive recording sheet, the side edges of the recording sheet are not available for image recording since the microcapsules on the side edges are ruptured by the feed rollers. Therefore, the use of the feed rollers has an economic disadvantage in that the photosensitive pressure-sensitive recording sheet must have an increased width so as to provide sufficient zones undergoing such feeding only, and also suffers a maintenance problem in that any photosensitive composition deposited on the feed rollers must be cleaned away.